This is probably the first post I've actually started but something is bugging me that I can't get off my mind. Last fall, I was running sort-of rich (940-950 mV) since I had just started my own prom-burning, but I still set a record-best of 14.86 at 91 mph in 75-degree dry air (track is at sea level - MIR). Last Friday, I ran a best of 15.5 at 87.2 mph in 68-degree very-humid air with O2's in the 960 range. This is the same chip (except for 2 degrees more timing in the mid-range) I ran a week ago on a chassis dyno. On the dyno, I gained 4 horsepower across the whole powerband (2800 to 5200 rpm) by leaning out my PE by 4% and my O2's were in the 908-912 range. The air then was somewhat humid, but it was also cooler, in the low 50's (degree F).

My questions are: how much power does an engine lose due to humidity? How 'bout air temperature? Would the engine run richer due to hotter and more-humid air since there is less oxygen available to be burned? The only major change since last fall is the replacement of a gutted cat with a high-flow Random Tech cat. I have a hard time believing that it would cost me 30-40 horsepower, especially since the engine still feels very strong, even after 130k miles. Thoughts? Comments?

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Greg Westphal
'87 IROC 305TPI/A4

 

Humidity does have a great effect but I do not know the correction factors. But there are calculation factors at some of the NHRA web sites to assist in getting the correction factors.

I know temperature is about 1% for every 10 degree Farhenheit change. That might account for 4-6 HP but not the 30-40 HP.

I know we've been discussing it but maybe the MAF system is not correcting for the intake temperature as well as it should. Time to start doing some Diacom data runs at various temperatures (and humidity) to see how it affects your BLM/INT.

I am still trying to see if there is some form of correction within the MAF system for MAT, but so far, I am still not able to find anything similar to the SD's system. I keep looking to see if anything "pops" up that you may wish to test to verify.

 

First off, the addition of water changes the basic formula of reaction. During the compression cycle the heat releases the H2O to simple H and O. H is a fuel and O is an oxidizer, in the right guantity, (ala Space Shuttle). During the reaction prossess they release energy so, there should be a slight gain in HP. trouble is intake tract routing.

Simple timing changes take care of most ambient air temp changes

Remember stock O2 are back pressure sensitive, to some degree, and that other then your running richer then Stoic are meaning less.

All boils down to what the engine wants. By keeping complete notes you find the tuning trends for YOU engine that work.

When FULLY tuned right, ambient temp and hum shouldn't make much of a change, or let me say for any given calibration, that is doumented. From 32dF to 90dF ambient air temps some cars like a variance of 4 degrees, and some 10. Again, it's wnat the engine wants